Currently, the normal walking and flexion and extension of knee joints of many patients cannot be achieved due to the damage of muscles and cartilaginous tissues. In this case, prostheses are required to be implanted to replace the knee joints to help the patients to stand, walk and flex and extend normally again. Although the artificial knee joints have been widely applied, the traditional artificial knee joint is not meticulous enough when simulating the action of a natural knee and hence the human body cannot act in position smoothly when using the prosthesis and often cannot act properly. Particularly when the flexion of the knee joint is simulated, the traditional artificial knee joint only pays attention to the flexion and extension between a femur and a tibia of the knee joint during the flexion but ignores the external rotation of the femur relative to the tibia during the flexion. Therefore, it is substantively very difficult to achieve proper flexion in position, and the prosthesis can even be damaged as the action does not comply with the physiological characteristic of the human body; moreover, even the femur and the tibia of the patient can be damaged as well, and hence the patient's condition can be worse.
However, the external rotation of the knee of the human body during the flexion must be smooth and the movement range cannot be too large, or else the patient would be hurt. At present, although the problem has been considered b those skilled in the art, an actual means for solving the problem cannot be put forward. In the process of the simulation of the external rotation of the femur relative to the tibia, not only the action must be smooth but also further external rotation must be stopped in time. If the external rotation cannot be stopped in time, the problem of dislocation wilt be caused and even the personal safety will be affected. Therefore, as no effective means can be provided so far, the prosthesis designer is afraid of this for exclusion of liability.